DE60117778T2 - Ceramic beads packed together as bone substitute material - Google Patents

Abstract

Adherent packed beds of ceramic beads, each comprising a ceramic body coated with a biodegradable polymer, and fabric bags containing such beads in a packed, self-supporting configuration. The polymeric coating provides some resilience to a packed bed of the ceramic beads, and prevents the beads from moving with respect to each other when placed under stress, leading to reduced breakage. The ceramic beads desirably are osteoconductive, and preferably are formed of a ceramic material that is resorbed during bone growth, such as hydroxyapatite, tricalcium phosphate, or mixtures of these materials. The beads may contain, either internally or on their surfaces or both, a bone morphogenic protein, and the latter may also be included in the biodegradable polymer coatings on the beads.

Description

Territory of invention

The This invention relates to coated ceramic beads that are so packaged can that they form a bone substitute material.

background the invention

A good bone healing and subsequent favorable bone reshaping depends on maintaining stability between bone fragments and from the maintenance of physiological Voltage levels. Successful bone graft procedures usually require an osteoconductive matrix that provides a scaffold for bone ingrowth, osteoinductive factors that provide chemical agents that induce and repair bone regeneration, osteogenic cells, which by their ability to distinguish between osteoblasts and osteoclasts, the basic building blocks for the Provide bone regeneration, and a substantially stable Implant site. current Bone graft materials include autographs, allografts and a Variety of artificial or synthetic bone replacement materials.

In order to structural bone repair materials are used in the usual way you can, you must can be shaped into complex shapes that are designed that they fit the contours of the repair site. Precisely contoured grafts improve the integration of natural bone and provide for one better resilience. An intimate stress contact between the natural Bone and the bone substitute material is often required to make a To support bone modeling and regeneration, the for collecting the grafts by the guest bone leads. One general overview of orthopedic implant materials is given in Damien, Christopher j. and Parsons, Russell J. "Bone Graft and Bonde Graft Substitutes: A Review of Current Technology and Applications, Journal of Applied Bio Materials, Volume 2, pages 197-208 (1991).

Bone substitutes have a special application in the repair of disc degeneration, and a method and apparatus for such repair in U.S. Patent Nos. 5,549,679 and 5,571,189. These patents describe a surgical operation in which a hole is lateral into a degenerate disk body is drilled, the hole in the body of the Bone vertebra is widened above and below the disc, so that one continues, as possible rounded cavity is formed. The doctor then carries a flexible cloth bag into the cavity and fills the bag with a particulate Bone substitute material. The preferred filler material can be as finely chopped chips of cortical or cancellous bone for the Fusion of hydroxyapatite or the like biocompatible Materials or connective tissue when a fiber combination is desired, identified. When the bag is fully packed, its mouth is closed and the surgical procedure becomes more common at the site Way repaired.

In Compound with the procedure described in the above patents experiments were carried out with the aim of passing the cortical or cancellous bone chips through others To replace particulate materials, including special ceramic beads. The beads can zircon, alumina, hydroxyapatite or another ceramic Material can be made and can be one have a substantially cubic shape, with the sharp edges of the cube are rounded. If ceramic beads This type can be packed tightly in a fabric bag the beads together rub and produce fine particles when they are relatively stable positions looking in relation to each other. About that can out the beads themselves Naturally break when exposed to packing forces are. Even if they are tight, they can the beads still in dependence shifting loads somewhat in relation to each other move until bone ingrowth stabilizes its positions. It is desirable to prevent such a movement, also insofar as that one such movement local Formations of a high voltage can generate, leading to a rupture of globule leads.

It would be desirable Ceramic beads too create that opposite a relative movement and a break are resistant when they for example in a cloth bag according to the teachings of the above patents packed together, and those beyond osteoconductive and osteoinductive materials, such as a bone morphogenetic Protein, to promote bone ingrowth.

Summary the invention

We have found that ceramic beads each having a ceramic body coated with a biodegradable polymer are particularly useful when used in the above-mentioned operation. The polymer coating provides some elasticity in a packed bed of ceramic beads and also helps to make the beads less friable as they move under tension. The ceramic beads are osteoconductive as possible and are preferably before a ceramic material which is absorbed during bone growth, such as hydroxyapatite, tricalcium phosphate or mixtures of these materials. The beads may contain either and / or on their surfaces a bone morphogenic protein and this may also be included in the biodegradable polymer coatings on the beads.

In structurally speaking the beads be firm and dense or porous be. Solid, dense spheres can a higher one Have elastic modulus and greater strength show as this is porous globule do. However, the lower modulus of elasticity of porous beads is the modulus of elasticity a natural one Bone much closer. porous beads which are useful in the present invention may include continuous, strong supportive Framework of aspirations that have a plurality of each other connected spaces which form pores that expand across their volumes and open on their surfaces. One Bone-morphogenic protein can absorbed in the pores and transported by these so this for support of bone growth is available. Thus, in one embodiment, the invention provides ceramic beads ready, when packed or grouped together, as a bone substitute material useful are. The beads each comprise a ceramic body with an outer surface, the one Form with mass volume forms. The outer surfaces of the beads carry a substantially continuous Coating a biodegradable polymer, wherein the coating a surface provides, which allows that the beads in a coherent, load-bearing mass can be packed together when exposed to compressive forces are, causing a breakage of globules due to rubbing together adjacent beads is avoided, the beads but they can move freely past each other if they are not compressed are. The polymer coatings provide the packed beads with a degree Elasticity, harmless shock forces to absorb, otherwise to fragility of the beads to lead could.

In another embodiment The invention relates to an article intended for replacement or the stabilization of a bone is useful. The item Includes a fabric bag made of a fabric with openings is formed, which are such that a bone growth through this possible is. In the bag are a plurality of ceramic beads of the type described above. At contact points between the beads keep biodegradable polymer coatings on the outer surfaces of the Globules the globule to slip past each other when they are in their packed Orientation in the bag. The coatings deliver as well a thin, elastic Surface with which the effects of sudden forces, such as compressing Shock forces, too dampen. The with the polymer-coated ceramic beads described Type-packed bags provide a stable implant structure that for spinal and other orthopedic procedures is usable.

As earlier mentioned, can the beads if necessary, a continuous, strongly supporting framework of struts having a plurality of interconnected spaces, which interconnected openings or form pores that extend through the entire volume and on the ceramic surface open the beads and preferably also open on the biodegradable polymer coating.

Summary the drawings

1 Figure 11 is a broken schematic view, partly in cross section, showing one step in the method of the invention for repairing spinal injury.

detailed Description of the preferred embodiment

The useful in the invention Globules can in Basically made of any biologically compatible ceramic material but are preferably made of such ceramic materials, the are osteoconductive, and in particular from those involved in the process of bone ingrowth can be absorbed. Suitable ceramic materials include hydroxyapatite, tricalcium phosphate and mixtures thereof. If necessary, you can the beads also contain one or more non-absorbable ceramic materials, such as zirconium or alumina. When the ceramic is absorbable is, for example, when a mixture of hydroxyapatite and tricalcium Phosphate is used, which results in healing Structure by the bone ingrowth assume a bone shape. If on the other hand, a proportion of the ceramic from a non-absorbable Material exists, such as zirconium, remains in the support structure a zirconium network, and this may give the bone structure the desired rigidity to lend.

The ceramic beads themselves may be solid, dense structures or may exhibit a varying degree of porosity. In one embodiment, the beads to which a coating is applied, as described below, have pores that extend throughout their entire volume. If possible, every bead egg ceramic body having an outer surface forming a mass volume shape and having a continuous high support framework of struts providing a plurality of interconnected spaces or pores. The beads of the invention preferably have a roundish shape, and although different sizes of beads may be mixed together and used in the invention, it is desirable that the beads have a substantially uniform size to provide good packing and to enable that continuous openings are maintained between the beads when they are packed together. That is, it is preferred to avoid the use of mixtures of globules of different sizes in which smaller beads can clog or severely narrow the openings between larger beads.

If porous globule used to form the inner, interconnected interspaces every globule openings, which extend through the entire volume of the bead and the on the surface open the beads, so that the pores from outside the beads are "accessible". The beads can be prepared so that they have pores of different diameters. Preferably, the beads are made with pores ranging from about 0.3 to about 50 microns.

Porous ceramic beads can be prepared by a process in which a viscous Sol of a polymer, such as cellulose, and a primary solvent, such as N-methyl-morpholine-N-oxide ("NMMO") when in contact with a secondary Solvent, such as water or alcohols, with which the primary solvent is miscible, but in which the polymer is not soluble, will coagulate if the primary solvent extracted from the sol, leaving an open polymer structure remains. Reference is made to U.S. Patents 4,246,221 (McCorsley), 4,416,698 (McCorsley), 5,252,284 (Jurkowic et al.) And 5,540,874 (Yamada et al.). See also U.S. Patent 3,508,941 (Johnson).

As in the co-pending US patent application, official file reference No. 09/286919 filed on Apr. 6, 1999 under the name "Sinterable Structures and Method " is, can sinterable Ceramic materials such as hydroxyapatite, tricalcium Phosphate, zirconium, alumina, etc., with the viscous sol of Polymers are mixed. Therefore, the mixture can be coagulated, such that a gel is formed by contact with a secondary liquid, in which the polymer is not soluble is and which is the primary solvent extracted and replaced, leaving a fine, open polymer network with the remaining in this arranged sinterable powder remains. The material may be suitably coated in fibers, sheets, hoses etc. molded, either in the form of the viscous sol (e.g. Extrusion) or by shaping the resulting gel.

From special usefulness Here is a method in which the viscous sol with the ceramic particles dribs and drabs is converted into a non-solvent for the sol, such as in a 50/50 volume percent water / NMMO mixture. The resulting roundish particles can be collected on a sieve dried in a drying oven and then slowly to sintering temperatures heated become. While the temperature rise becomes the organic sol material by pyrolysis removed, leaving a network in contact with each other sinterable Ceramic particles remains. After all, when the material is brought to sintering temperatures, the sinter still in a configuration determined by the configuration of the gel ceramic particles such that strong, round, porous, self-supporting ceramic beads be formed. These beads, with pores in a diameter range of about 0.3 to about 50 microns and an extension through the whole volume of the beads, are essentially different from the semi-porous product, resulting from the simple sintering of ceramic pressed into molds Powder results. In the latter case, the pores or openings, the initial between the particles are present, smaller and closed, when the particles grow together sufficiently to be self-supporting To form ceramic structure, wherein the pores optionally as far as possible melted as the density of the material increases.

In any event, the porous ceramic beads useful in the invention can be prepared by first preparing a viscous mixture comprising a sinterable ceramic powder or mixture of powders such as ceramics such as hydroxyapatite, tricalcium phosphate, zirconium, alumina or the like; in a sol of a polymer, such as cellulose, in a primary solvent, such as NMMO, the primary solvent is replaced by a secondary liquid in which the polymer is insoluble (such as a water / NMMO mixture) to form a gel with an open polymer network having the sinterable powder in it, the secondary liquid being removed from the gel and the product being brought to sintering temperatures to remove the polymer structure and form the desired open, porous ceramic structure. As previously mentioned, it is desirable that the viscous mixture with the Ke ramikpulver and a primary solvent is added to the secondary solvent as droplets, so as to produce a roundish particle.

The porous Interior of the ceramic particles described above may be at least partially be filled with a bone-morphogenic protein to the formation of new To induce bone mass. A bone-morphogenic protein is without Other available from commercial sources and a special bone morphogenes Protein BMP-7, sold as OP-1 by Stryker Biotech, a division of Stryker Corp., is for suitable for this purpose. Bone morphogenetic protein can be found throughout the pore volume of the bead be contained, and in this embodiment it is important that is the pores of the bead extend completely through the volume of the bead and on the surface of the bead accessible and are open.

The Use of bone morphogenic protein in combination with ceramic Materials have been described in U.S. Patent 4,596,574 (Urist), wherein the ceramic materials there by a powder sintering technique be formed. The teachings of Urist's' 574 patent are incorporated herein by reference recorded with. In connection with beads of the invention bone-morphogenic protein in Form of a powdered Solid with the beads either before or after application of the biodegradable Polymer coating are combined, and by pushing / moving (as by a ball mill) the powder can be applied to the coated or uncoated spherical surfaces or, if applied before the polymer coating, at least partially incorporated within the pores of the beads. It comes into consideration that bone-morphogenes protein powder under Use of electrostatic attraction techniques on the beads can be applied, in which the beads and the powder particles given opposite charges.

The bone-morphogenic protein can in the beads by various techniques using liquid or gel-like vehicles are incorporated. For example, a bone morphogenetic Egg white powder, like BMP-7, in a saline solution solved can and can porous beads suitably with the solution be brought into contact, such as by immersion, with it the solution into the pores can occur. The penetration of the solution in the pores can be relieved by pulling a vacuum, so that the beads degas and the solution the escaped gas (e.g., air) in the beads is replaced. The beads can then dried so that a residue of the protein remains in the pores. If necessary, the protein solution in the beads remain when they are introduced into the bag, or the solution can globule added if they are already in the bag, for example through the use of a suitable syringe. In general are The pores of the particles are so small that the solution readily in the pores retained by capillary action becomes. If the retention of the solution in the beads by capillary action is insufficient, biologically compatible Thickening agents, such as a collagen, chitosan, or a Polymer, such as a poly (vinyl alcohol) or methyl cellulose, into the solution be inserted to their viscosity to increase. Concentration of bone-morphogenic protein in Pores can be increased be repeated by repeating the beads with a solution bone-morphogenic protein be contacted and then dried to the solvent to remove.

The ceramic surfaces carry the beads a coating of a biodegradable polymer material. The preferred biodegradable polymers are poly (lactic acid) ("PLA") and poly (glycolic acid) ("PGA"). Preferably a lactic acid / glycolic acid copolymer from approximately equimolar Quantities of lactic acid and glycolic acid monomers the rate of biodegradability is a function the rate of these monomers is. The polymers themselves can be used on the surface the ceramic beads deposited by any suitable means. In a preferred Coating methods can be used globule in an upward direction flowing Gas are brought into suspension to form a fluidized bed. A fine spray a solution the biodegradable polymer is introduced into the fluidized bed, being fine droplets the solution the ceramic surfaces taken up the beads be to the beads to coat, and the solvent through the continued flow gas from beads is evaporated.

Alternatively, the polymers may be applied from a solution, for example, prepared by preparing a solution of a biodegradable polymer or from polymers in a suitable solvent such as methylene chloride. The beads are pulled out of the polymer solution after a few seconds. When porous beads are used, the time during which the beads remain in solution depends on the penetration of the polymer solution into the pores of the beads. After removal from the solution, the beads may be placed on a sieve or other suitable support capable of keeping the beads separate. The use of egg A wire or polymer mesh sieve allows the beads to be supported in separate mesh apertures to prevent beads from adhering to one another. The coated beads can be air dried with anhydrous air and stored in a desiccator.

The Coating on the beads is applied is essentially continuous. A complete cover is natural not mandatory. In the case of porous beads, part of the biological degradable polymer solution absorbed in the pores and can open the pores themselves through the coating. The Coating on the exterior of the globule is in any case essentially complete and may be in thickness from about 50 to about 200 nm, based on the weight gain the beads that resulting from the coating process and SEM estimates. So is in the case of porous beads the thickness of the coating is preferably less than the diameter the pores, and more preferably at least an order of magnitude lower than that Pore diameter.

If necessary, may be a bone-morphogenic protein in the polymer coating be included to aid bone ingrowth. This can be brought about by removing the bone-morphogenic protein in a solution of the polymer material is used, the solvent system uses both the bone morphogenic protein and the biodegradable Polymer, such as a poly (glycolic acid). As noted above bone-morphogenic protein too be incorporated into the coating by simply using this as a dry powder is applied to the coated surface of the beads, and such a coating on the coating before it has completely dried out, may prove beneficial. An impact / stirring, as by a ball mill, the droplet with added powder, can also help the protein powder at least a little bit in the coating, so that only Little of the powder is lost when the droplets are transferred in a bag.

The biodegradable, polymer coated surfaces of globule allow, if they are dry, that the beads can easily slip past each other when, for example from a container poured into another become. The coating protects the beads before a break and fragmentation of the bed, as in the filling and Packing process. If the beads not be deposited under pressure by compacting them, they will continue to flow without further ado. However, once the beads are packed together are and are subjected to a compressive force, as in the Cloth bag used in the above-mentioned spinal surgery occurs will, leads the polymer coating on the beads cause the beads can stick to each other. It is believed that the polymer coatings at contact points the beads merge and so the beads enable it to agglomerate into a coherent mass or to be packed together.

By the use of round globules, preferably with a fairly uniform diameter a winding passage between the packed Kü gelchen receive. Of importance is that the coatings the beads enable them to be easily pourable and on the one hand to arrange in this way even to a densely packed mass, but as soon as the beads are tightly packed and thus under a certain compression The coating serves to prevent the beads from rubbing against each other withhold and thus breaking or pulverizing the beads to minimize. About that lead out the coated beads, when they are packed together, to cling to each other and the packed mass of beads a degree of elasticity to rent.

The globule themselves preferably have sizes in the range from about 1 to 5 mm and are, as already noted, preferably essentially roundish. It is also desirable that the beads be used in a bag procedure, as now described, of uniform Size are around to facilitate packing, and also to an open passageway upright between the beads to obtain.

The use of beads of the invention in a surgical procedure is described in U.S. Pat 1 exemplified and shown. 1 shows a section of a spine commonly associated with 10 is designated, the spine of alternating vertebrae 12 . 14 . 16 and slices 11 . 13 . 15 is formed. For the purpose of illustration, we assume that the disk 13 has suffered a degeneration.

In accordance with the procedures outlined in Kuslich, US Patent 5,549,679, a hole is made 18 through the annulus fibrosis 30 or the outer wall of the disc formed therethrough, wherein the hole between the vertebral bodies 14 and 16 extends. The depth of the hole extends almost through the width of the disc, but ends just before the distant wall of the annulus fibrosis 30 the disc. A hole diameter of about 10 mm is suitable, and the depth of the hole may be on the order of, for example, about 25 mm when the disc being operated on lies between the fourth and fifth lumbar vertebrae in the spine of a typical male adult. The diameter of the chamber is then increased by cutting a shallow cavity into the vertebrae immediately above and below the disc, forming the chamber as shown in FIG 1 is shown so that it is spherical or substantially roundish shape. Enlargement of the cavity without increasing the size of the entrance hole is desirable in terms of uptake and stability of the implant. An expansion cutting tool of the type shown in Kuslich, US Patent 5,062,845, may be used, the teachings of which are incorporated herein by reference. Enlarging the lumen, as outlined in Kuslich '679, also provides a necessary step for removing degenerated disc material and exposing the bone in the vertebral bodies to increase the likelihood of successful graft incorporation. It will be clear that the operation described so far can be performed with anterior or posterior surgical procedure.

In the thus prepared, expanded chamber 20 becomes a porous bag 22 with a shape that, when inflated, is substantially the same as the shape of the chamber 20 which is a bit bigger than the chamber. In the upwardly open mouth 24 The bag is an insertion tube 26 are arranged, and through this tube, the beads of the invention, generally with 28 designated inserted in the bag. The continuous addition of beads causes the bag to intimately contact the walls of the chamber 20 to expand, with the beads flowing past each other into a densely packed configuration. As the bag expands, its outer surfaces abut correspondingly against the opposing surfaces of the vertebrae 14 . 16 , below or above the disc 13 lie. Continuous expansion of the bag causes the vertebrae to loosen slightly and the annulus fibrosis to separate 30 the disc 13 narrowed in this way. The beads 28 flow when in the bag 22 Enter, without further passing each other, so that they take the inside of the bag completely. Blood, marrow or finely chopped pieces of bone, separately or in combination, may also be added to the pouch during the filling process as needed. This may help to provide autogenous osteoconductive and osteoinductive materials at the implant site. When the bag is completely filled with beads and packed, the mouth opening becomes 24 the bag sealed, such as with a drawstring (not shown) or the like.

Of the Fabric bag can be made of polyester or another suitable organic compatible material be prepared. Under 'fabric' is both a Tissue structure as well as a film or sheet-like structure with in the walls trained perforations understood. The substance can be sufficient be flexible so that this one is able to put it together and to be introduced into the cavity formed between adjacent vertebrae, but must be strong enough to avoid tearing or splitting if he is with beads filled the invention is.

The beads, as packaged in the bag, form a stable, non-moving mass, which in the preferred embodiment of porous beads exhibits porosity at two levels. First, the mass of substantially round globules that are packed tightly provides a series of gaps between the beads and allows body fluids and possibly bone mass to penetrate completely through the bag contents. Second, the beads themselves, when porous, may advantageously carry bone morphogenic protein or other bone growth material, and thus may provide such bone growth materials in place of the desired bone growth. So form the beads as they enter the chamber 20 a solid, coherent body wherein the biodegradable polymer coatings at contact points between the beads serve to retain the beads, move past each other under a sliding or varying load, and thus prevent breakage or pulverization of the beads beads.

In the following non-limiting Examples were coated ceramic particles in a polyester bag packed and subjected to repeated mechanical stress. For each The example became so coated and uncoated (control) particles tested.

example 1

Sintered ceramic dice of hydroxyapatite, about 2 mm in size, which had been partially rounded by treatment in a vibratory mill, were supplied by Ceramed Co. The density of the cubes was greater than 98% of the calculated size. These were coated by immersion in a solution of 0.75 grams of a copolymer of equal proportions of PGA and PLA (Alkermes Corp.) dissolved in 10 cc of methylene chloride. The coated cubes were drum-dried on a metal wire in dry air for 10 minutes and stored in an argon-filled desiccator. The coated cubes did not stick together. The polymer is in Essentially firm but elastic. The cubes were later inserted into a polyester cloth bag about 1 inch in diameter using a mechanical tool which tightly packed them by means of a shock and vibration load. The particle-filled pouch was subjected to intense mechanical stress and 1 million cycle deflection using a Enduratec biaxial test machine which applies both compressive and torsional loading to the samples.

Example 2

example 1 is repeated, except that the ceramic cube out Zirconium manufactured by Coors Corp. is delivered.

Example 3

example 2 is repeated, except that the solution is 1.5 Gram of PGA / PLA copolymer in 10 cc of methylene chloride.

Example 4

example 2 is repeated, except that the ceramic cube off Porcelain made by Continental Clay Col, Minneapolis, Minnesota, is delivered.

Example 5

In A 150 ml beaker contains 70 cc of N-methylmorpholine oxide / water a weight-dependent 50:50 Mixture filled. Using a stir bar on a magnetic stirrer heating mantle the mixture is stirred at a medium stage while 2.6 g of the powdery Cellulose (Aldrich Chemical Company) with an average particle size of 20 microns added becomes. The mixture is then heated and stirred to give a uniform, clear, forming a viscous orange sol. While this sol is still hot, 15.0 g of a powder containing 85% by weight of hydroxyapatite are added ("HA") and 15% tricalcium Contains phosphate ("TCP"), and stirred into the viscous sol, until a uniform suspension formed by the elimination of hydroxyapatite lumps and by an overall uniform, milky white Appearance is recognizable.

The resulting material is transferred to a syringe, and the material is drop by drop placed in a water bath. Become essentially roundish particles formed in the water and the water replaces the N-methylmorpholine oxide. The resulting roundish particles are dried at 50 ° C on a wire grid and are then removed from the wire grate holder and heated to 1200 ° C, to pyrolyze the cellulose and the hydroxyapatite / TGP ceramic to sinter. The resulting product is a strong microporous, ceramic roundish globule with a diameter of about 2 mm. The particles are then coated and tested as in Example 1.

Example 6

example 5 is repeated, except that the composition the ceramic beads 65 wt% HA and 35 wt% TCP.

Example 7

roundish Particles prepared as in Example 6 were placed in a aqueous saline solution dipped, which contains a red dye. The beads were going there tested whether they revealed and were the penetration of the dye balanced before and after to increase the amount of absorbed solution determine. In this open-pore globule (about 40% porosity) were essentially all pores filled with the solution.

Example 8

Around an optical detection over the degree of adhesion of the powdery bone morphogenetic protein to the surface To deliver the particles were roundish particles, as in the Example 6 were prepared in an iron (II, III) oxide for 30 seconds tumbled to apply the powder to the PGA / PLA coating on the beads. (10 grams of powder on 2 grams of beads). Methylene chloride (1 wt%) was mixed with the black powder before Drums in a ball mill mixed. Almost all of the black powder adhered to the ceramic Beads.

Results

It It is believed that it is of great importance to use the particulate materials while to prevent the bone healing process from relating to each other to move when they are under physical stress. A such stability is important with the progress of the bone repair process, until the ingrown natural Bone takes over the stabilization function. A break of the Can beads to a loss stability lead the packed bed; the resulting pieces and dust particles can Fill gap spaces that for the in growing bones are necessary and it is believed that finely powdered HA can interfere with osteogenesis.

In The bags were repeated after each of the above examples Torsion and compression loading in terms of ball adhesion and in terms of ball breakage and the undesired formation of powdered ball fragments examined.

Our Examination of the coated beads each example showed that the beads stuck together stay; you had to take them out of the bag break loose. In contrast, it was called uncoated beads used, no adhesion observed, and the beads were loose in the bag.

initial Tests with porcelain particles showed about a two-fold decrease of brittleness (measured in percent globules, which were broken) from coated to uncoated. The rounded ones HA and zirconium cubes showed a 2- to 4-fold decrease in brittleness, coated versus uncoated. The porous ones globule from HA / TCP compositions showed up to a ninefold decrease the brittleness, coated across from uncoated, with less than 1% of the beads showing damage at all.

Claims (13)

Ceramic beads ( 28 ), which can be used together as a bone substitute material, the beads ( 28 ) each have a ceramic body having an outer surface which carries a substantially continuous coating of a biodegradable polymer which, in the dry state, allows the coated beads to flow freely past each other but which causes the beads to form a coherent, loadable mass when subjected to compression forces to restrict breakage of beads due to rubbing of adjacent beads. ceramic beads according to claim 1, wherein the ceramic body is a continuous, strong supportive Framework made of struts that covers a plurality of each other connected spaces provides which delimit interconnected openings that are extend through the whole volume and through the ceramic surface of the globule open through it. ceramic beads according to claim 2, wherein the interconnected openings through Open the biodegradable polymer coating. ceramic beads according to any one of the preceding claims, wherein the ceramic body is osteoconductive is. ceramic beads according to any of the preceding claims, wherein the ceramic body comprises hydroxyapatite, Tricalcium phosphate or a mixture thereof. ceramic beads according to claim 5, wherein the ceramic body also a non-absorbable ceramic includes. ceramic beads according to claim 2 or any claim dependent thereon, having a bone-morphogenic protein, which is carried within the interconnected openings. ceramic beads according to any one of the preceding claims, wherein the shape of the ceramic body in Is essentially roundish. ceramic beads according to any one of the preceding claims, with a bone morphogenic Protein, that on the surface the coating is worn. ceramic beads according to any one of the preceding claims, wherein the coating not more than about a micrometer thick. Article for use in the replacement of a bone in orthopedic procedures, the article comprising a fabric bag ( 22 ) formed of a fabric having apertures sized to allow bone growth therethrough, the bag ( 22 ) a plurality of packed ceramic beads ( 28 ), each having a ceramic body having an outer surface forming a shape with a mass volume, wherein the outer surfaces of the beads ( 28 ) carry a substantially continuous coating of biodegradable polymer, the coating allowing the beads ( 28 ) form a coherent loadable mass when subjected to compressive forces to limit bead breakage due to rubbing adjacent beads together. Article according to claim 11, in which the beads ( 28 ) are packed together so that they have a plurality of openings between the beads ( 28 ) and in which the coatings fuse at contact points between the beads. Article according to claim 11 or 12, in which the beads ( 28 ) in accordance with any one of claims 1 to 10.